1. Field of the Invention
The present invention provides a system and apparatus for a low cost, long range, power efficient wireless system that provides identification and locational information.
2. Description of Related Art
The wireless Local Area Networks (LAN), based on the 802.11(a/b/g/n) standard, support short range communications between portable devices such as notebooks. The system design employs Time Division Duplex (TDD) and Orthogonal Frequency Division Multiplexing (OFDM) modulation that is optimized for high data throughput in an indoor fading environment. In order to fairly share the wireless medium among different devices, the network protocol tries to keep a single node from occupying the medium for a long period of time by limiting the lowest allowable signaling rate. Since the required signal-to-noise ratio for a given bandwidth is proportional to the signaling rate, the achievable communication range for a wireless LAN is limited.
Wide Area wireless Networks (WAN), such as cell phone networks, on the other hand, are optimized for a larger number of users and longer range. The system design employs either Frequency Division Duplexing (FDD) or Time Division Duplexing (TDD) and wideband Code Division Multiple Access (CDMA) or OFDM modulation to support a variety of services including high peak data traffic, continuous low rate voice traffic, continuous broadcast multimedia traffic, and short data bursts for paging messages. A cell phone base station with 40 watts of transmission power and an antenna at the top of a tower can provide a coverage area in excess of 2 miles in diameter. This long range communication is achieved primarily by the placement of the base station antenna at the top of the tower to overcome the signal loss due to building blockage. A typical cell phone battery can last for a few hours of continuous use and a week of stand-by time. The cell phone network also provides security against illegal access to the network and eavesdropping, but does not protect against unauthorized radiators within the band and/or jammers.
ZigBee is a specification based on the IEEE 802.15.4 standard for low cost, low power, wireless mesh networking. The targeted application is wireless control and monitoring. The low power usage of ZigBee devices allows a longer battery life and smaller batteries. The mesh networking attribute provides higher reliability and longer range. Because ZigBee can be activated (going from sleep to active mode) in 15 msec or less, the latency can be very low, and devices can be very responsive, particularly compared to Bluetooth, which has delays in waking up that are typically around three seconds. Since ZigBee is in sleep mode most of the time, its average power consumption can be very low, resulting in a longer battery life.
In beacon-enabled networks, special network nodes called ZigBee routers transmit periodic beacons to confirm their presence to other network nodes. Nodes sleep between beacons, thus lowering their duty cycle and extending their battery life. Beacon intervals range from 15.36 milliseconds to 3.287 seconds at 250 kbit/s, from 24 milliseconds to 5.136 seconds at 40 kbit/s and from 48 milliseconds to 10.272 seconds at 20 kbit/s. However, a low duty cycle operation with long beacon intervals requires precise timing, which is in direct conflict with the need for a low product cost. Alternatively, in non-beacon-enabled networks, an unslotted Carrier Sense Medium Access/Collision Avoidance (CSMA/CA) channel access mechanism can be used. In this type of network, ZigBee routers typically have their receiver continuously in the active mode, which requires a more robust power supply. However, this allows for a heterogeneous network in which some devices receive continuously, while others only transmit when an external stimulus is detected. Thus, longer battery life is achievable by one of two means: a continuous network connection and a slow but steady battery drain, or an intermittent connection and an even slower battery drain. To keep the power consumption requirements low in ZigBee devices, the expected range is from 10 to 70 meters.
For wireless systems that provide identification and location information, there is a need for security, long range, high mobility, and near full connectivity with acceptable latency using low cost, low power, compact and light weight devices.